The present invention generally pertains to apparatus and methods used in underwater maintenance and construction and is particularly directed to improvements in underwater gas pocket work units and their use.
An underwater gas pocket work unit is described in Applicant's U.S. Pat. No. 4,288,176. The work unit is adapted for attachment to an underwater work surface to define a work chamber that may be entered from beneath through the water. The work unit includes a structure consisting of continuously joined side walls, and is open at both the top and the bottom. The structure is sealed at the top opening to the work surface, such as the bottom of a ship, to provide a work chamber that is defined solely by the structure and the work surface. A valve is provided through the structure for enabling a gas, such as air, to enter the work chamber to provide a gaseous pocket in the upper portion of the work chamber when the structure is sealed to the underwater work surface. A vent port is provided in at least one of the side walls at a predetermined level that is more remote from the top end of the structure than the valve for enabling gas to flow from the gaseous pocket into the water outside the work chamber when the top end of the structure is sealed to the underwater work surface to thereby define the water level within the work chamber and limit the maximum depth of the gaseous pocket. The side walls of the structure each contain both inner and outer walls defining floatation chambers into which air may be admitted to control the buoyancy of the structure so as to force the work unit up against the work surface. A resilient gasket is provided at the opening at the top end of the structure to effect a seal between the structure and the work surface when the work unit is forced up against the work surface. Such prior art work unit is limited in its application to use with work surfaces that do not deviate greatly from the horizontal.
A safety concern that has arisen in relation to the use of underwater gas pocket work units is the maintenance of a habitable environment in the work chamber when the nature of the work is such that dangerous fumes and gases are produced therein.